0.1 second is about the limit for having the user feel that the system is reacting instantaneously, meaning that no special feedback is necessary except to display the result.

1.0 second is about the limit for the user’s flow of thought to stay uninterrupted, even though the user will notice the delay. Normally, no special feedback is necessary during delays of more than 0.1 but less than 1.0 second, but the user does lose the feeling of operating directly on the data.

10 seconds is about the limit for keeping the user’s attention focused on the dialogue. For longer delays, users will want to perform other tasks while waiting for the computer to finish, so they should be given feedback indicating when the computer expects to be done. Feedback during the delay is especially important if the response time is likely to be highly variable, since users will then not know what to expect.

Jakob cites Miller’s “Response time in man-computer conversational transactions” – a paper that dates back to 1968. It seems like in more than forty years the consensus about acceptable response times has not moved substantially – which could be explained by the numbers being determined by human nature, independently of technology.

But still, I am rattled by such unquestioned consensus – the absence of dissenting voices could be interpreted as a sign of methodological complacency.

Indeed, but points us to how to collect our own data on the subject; and I think is pretty good on methodology. Anybody with high enough traffic can test it.

In my own totally informal testing on Club-Internet home page, I know that somewhere around 7+ secs to load the home as perceived by user (for a day or so) would significantly reduce traffic (20%ish at least), this is about 5 years ago.